Intercommunicating circuit



Aug. 12, 1941, R. c. BRADFORD ETAL 2,252,549

INTERCOMMUNICATING CIRCUIT Filed July 23, 1940 S 5 l ,L I a ,5

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INVENTORS B. C Bradford 1 BY (Z Cl is Patented Aug. 12, 1941 Clifford Clark, West Haven, Conn; assignors to American Telephone and Telegraph Company,

a corporation of New York Application July 23, 1940, Serial No. 346,966

Claims.

This invention relates to intercommunicating circuits by which one subscriber may telephone to another, and more particularly to signaling arrangements to be used in connection with said circuits. It is an object of the present invention to provide an intercommunicating telephone circuit so arranged that either subscriber may signal the other by the use of a minimum amount of apparatus.

It is a further object of the invention to provide a signaling arrangement of the kind above described which is so designed that when one subscriber hangs up before the other at the end of a conversation, a false signal will not result.

The invention may now be more fully understood by reference to the accompanyingdrawing at station S2 being designated B2.

The invention will now be morereadily understood from a description of its.operation, which is as follows: 1

Let us assume, that r the subscriber S1 desires to call the subscriber.S2.; By closing the controlling switch at his station, subscriber S1 causes current to flow from the positive lead of the battery through the upper winding of relay SR1, over the conductor T1 to subscribers station S1, and thence back over the conductor R1 and through the lower winding of relay SR1 to the negative side of the battery. This energizes the relay SR1, which at its outermost upper contact closes a. circuit from ground over the innermost lower contact of relay SR2, and over the contact and through the winding of buzzer B2 tobattery. The buzzer B2 now operates and the subscriber at station S2 is informed that he is being called.

Upon the subscriber at station S2 operating his switch to answer the call, current flows from the positive conductor of the battery leads BL, through the upper winding of relay SR2, over the conductor T2 to the subscribers station S2, and

back over the conductor R2, and through the lower winding of relay SR2 to the negative side of the battery. This energizes relay SR2 which at its innermost lower contact now opens the circuit 5 previously described for the buzzer T2, thus bringing the signal to an end. At its outer upper contact relay SR2 prepares a circuit for the buzzer B1, but this circuit is held open at the innermost lower contact of the relay SR2 which is already energized.

It, will be noted that as soon as both relays SR1 and SR2 are energized the conductors T1 and R1 are directlyconnected to the conductors T2 and R2 over the innermost upper contacts and outermost' lower contacts of relays SR1 and SR2, and that talking battery is now supplied to both subiers station S2.

stations through the impedances of the windings ofsaid relays.

It will also be evident that by means of the connections just described the relay SR1, whose circuit was completed at the subscribers station S1, is locked up over the contact at the subscrib- The circuit may be traced from the positive conductor of battery leads BL through the upper winding of relay SR1, innermost upper contact of relay SR1, innermost upper contact of relay SR2, over the conductor T2 to substation S2, and thence back'over the conductor R2, over the outermost lower contact of relay SR2, outermost lower contact of relay SR1, and thence through the lower winding of relay SR1 to negative battery.

In a. similar manner the relay SR2, which is normally energized over the contact of the station S2, is locked up over the contact of the'station S1, the connections being as follows: From positive conductor of battery leads. BL, through the upper winding of relay SR2, innermost upper contact of relays SR2 and SR1, over the conductor T1, through the subscribers station S1, back over the conductor R1, over the outermost lower contacts of relays SR1 and SR2 and thence through the lower winding of relay SR2 to the negative side of the battery.

These locking circuits prevent false operation of the signals when the subscribers hang up. For example, if the subscriber at S2 hangs up, the relay SR2, controlled by his station, will not be released as it is locked up over the circuit, just described which is controlled by the substation S1. As long as the circuit at station S1 is closed both relays SR1 and SR2 will remain energized. When both of these relays are energized both buzzer circuits are held open at the innermost lower contacts of said relays. As soon, however,

as the subscriber at station S1 opens his switch, relay SR1 releases (the previously described locking circuit through relay SR1 was opened at the contact of the subscribers station S2) and the relay SR2 is deenergized at the same time because the locking circuit for said relay over the contact of the substation S1 is opened. Both relays, therefore, release at the same time and no false signal by either buzzer is possible.

It will be obvious, of course, that if no locking circuits had been provided for relays SR1 and SR2, and the subscriber at S2 released his circuit before the subscriber at S1 hung up, relay SR2 would have been released while relay SR1 still remained energized, with the result that the circuit previously traced for the buzzer B2 would be actuated. Similarly, if the subscriber S1 released his circuit ahead of the subscriber S2, relay SR1 would be deenergized while relay SR2 would re main pulled up, thus completing a circuit for the buzzer B1 over the outermost upper contact of the relay SR2 and the innermost lower contact of the relay SR1.

To recapitulate: When both subscribers circuits are completed, relays SR1 and SR2 are each locked up over contacts of both relays through opposite subscribers sets. If one subscriber hangs up ahead of the other, the locking circuit of the relay of the other subscriber is opened, but

the normal energizing circuit of said'relay is still closed by the opposite subscriber. The subscriber first hanging up cannot release his own relay because it remains locked up over the contacts of both relays and over the contact of the opposite subscribers set. Therefore, no false operation of the signal can take place. When, however, the opposite subscriber releases his-circuit, both relays are released simultaneously and the apparatus is in normal condition.

It will be obvious that the general principles herein disclosed may be embodied in many other organizations widely different from those illustrated without departing from the spirit of the invention as defined in thefollowing claims.

What is claimed is:

1. In a telephone system, a line, a station at each endthereof, relay means for each station respectively actuated by closure of the line thereat, a signal device at each station responsive to actuation of the relay means of the distant station and disabled in response to actuation of the near relay means, and means effective upon actuation of both relay means to maintain both relay means actuated until the line is opened at both ends.

2. In a telephone system, a pair of stations, a line therebetween and terminating in normally open switch contacts in said line at each station, a relay for each station having a winding in series with the line, a source of direct current in bridge of said line intermediate said relays, said relays being adapted to individually operate in response to closure of the respective station switch contacts, a signal device at each station adapted to be actuated in response to operation of the relay of the distant station and disabled in response to operation of the near relay, and means effective upon operation of both relays to maintain both relays operated until the switch contacts at both "each station, a signal device at each station, said relays so controlling said signal devices that when one of the relays is actuated from one of the stations the signal at the other station will be operated until the other relay is actuated from said other station, and means effective upon actuation of both relays to maintain both relays locked up so that neither can be released until the line is opened at both stations.

4. In a telephone system, a pair of stations, a line therebetween, a pair of relays associated with said line and adapted to be operated one from each station, a signal device at each station, said relays so controlling said signal devices that .--When one of the relays is actuated from one of the stations the signal at the other station will be operated until the other relay is actuated from said other. station, and means effective upon actuation of both relays to lock up said relays so that whenthe line is opened at one station the relay controlled thereby will remain locked up through the other station, and both relays Will be simultaneously released when the line is opened at said other station.

5. In a telephone system, a pair of stations, a line .therebetween, a pair of relays associated with said line and so arranged that talking battery .is supplied to said line through the impedance of said relay windings, said relays adapted to be operated one from each station, a signal device at each station,.said relays so controlling said signal devices that when one of the relays is actuated from one of the stations the signal at the other station will be operated until the other relay. is actuated from said other station, and means effective upon actuation of both relays to maintain both relays locked up, so that neither can be released until the line is opened at both stations.

RAYMOND C. BRADFORD. GEORGE C. CLARK. 

